1. Field of the Invention
The invention relates to a centrifugal bowl separator, sometimes referred to as a solid bowl centrifuge.
2. Prior Art
The broad concept of using a packet of conical discs in a centrifugal bowl separator is well known. They enhance the clarifying capability in that they separate the material being treated into a multiplicity of layers moving between the individual discs, and thus they shorten the length of the precipitation path for the denser substances. Such packets of discs are particularly suited for the separation of substances having a low precipitation rates such as yeasts, bacteria and the like. During the settling operation, the substances to be separated must be conducted in such a manner that turbulences are avoided, or else there would be a danger that particle already settled would be entrained into the flow of the lower density substances, whereby the separating capability of the centrifuge would be adversely affected.
A conical disc insert for centrifugal drums is shown in German Pat. No. 25 45 754 which discloses normal discs and intermediate discs which form ascending channels disposed at a distance from the axis of rotation near the outermost area for the distribution of a liquid containing solids to the spaces between the individual discs. With this arrangement, the intermediate discs have a smaller inside diameter than the normal discs. In such apparatus, the coarser solid particles are immediately removed from the rising channels into a space where solids are collected, but the finer solid particles are entrained into the spaces between the discs by the partially clarified liquid which is flowing downwardly, whereby, as a function of the settling rate, sedimentation at the lower side of the next highest normal disc can occur at various locations along the flow path of the liquid. With this arrangement, the inner radial area at the intermediate discs between two normal discs has a counter-flow of solids and liquids, whereby turbulences are unavoidable.
A further conical disc insert for a centrifuge is shown in German Pat. No. 650,595. In this structure, the discs form ascending channels for the substances to be separated in an area adjacent to the axis of rotation. The solids centrifuged onto the upper side of a disc and the clarified liquid thereabove thereby flow in co-current flow with respect to one another proceeding from a radially inside area. At a radially outside area, the discs have a series of aligned openings, surrounded by collars and forming discharge channels for the clarified liquid. The collars function to protect the flow of solids moving toward the outside from turbulence due to the ascending liquid stream. However, as a function of the thickness of the layer of solids sliding over the disc, as well as its grain size and settling rate, turbulences and the like can hardly be prevented due to the pressure distribution to be expected in the proximity of the collars.